The effect of zirconium ions on glass structure and proton conductivity was investigated for sol-gel-derived P2O5-SiO2 glasses. Porous glasses were prepared through hydrolysis of PO(OCH3)(3), Zr(OC4H9)(4), and Si(OC2H5)(4). Chemical bonding of the P5+ ions was characterized using P-31-NMR spectra. The phosphorous ions, occurring as PO(OH)(3) in the ZrO2-free glass, were polymerized with one or two bridging oxygen ions per PO4 unit with increased ZrO2 content. The chemical stability of these glasses was increased significantly on the addition of ZrO2, but the conductivity gradually decreased from 26 to 12 mS/cm at room temperature for 10P(2)O(5).7ZrO(2).83SiO(2) glass. A fuel cell was constructed using 10P(2)O(5).5ZrO(2).85SiO(2) glass as the electrolyte; a power of similar to4.5 mW/cm(2) was attained.